Add the ability to create multiple event groups, each with their own leaderusing the existing "-e <event>[,<event> ...] [-e <event>[,<event>]]"syntax. Each additional -e switch creates a new group, and each eventlisted within a -e switch is within that group.

Changes since v1:- Because of a flub, v2 did not contain the changes I had intended to make,and instead, v2 had the same patch contents as v1.- When perf stat is not supplied any events on the command line, puteach default event in its own group.

DESCRIPTION -----------@@ -28,7 +28,13 @@ OPTIONS Select the PMU event. Selection can be a symbolic event name (use 'perf list' to list all events) or a raw PMU event (eventsel+umask) in the form of rNNN where NNN is a- hexadecimal event descriptor.+ hexadecimal event descriptor. As shown, multiple events can be+ separated by commas in each -e/--event switch. Each additional+ -e/--event switch creates a new event group. Grouped events are+ scheduled onto the PMU hardware at the same time, which is+ important to know when the PMU is overscheduled. A good example of+ this is measuring CPI where both instructions and cycles events+ need to be scheduled simultaneously to get an accurate estimate.